The advantages of using endoscopic visualization during surgical procedures on patients are well known. Such procedures are minimally invasive, result in shortened hospital stays, more rapid recovery, less cosmetic damage, and lower overall costs compared to conventional "open" procedures.
Surgical endoscopic instruments and procedures are also well known for removing a section of a blood vessel from a surgical patient for use in another part of the patient's body or for transplanting into a second patient's body. An endoscope and method for vein removal is described in U.S. Pat. No. Re. 36,043 issued to Knighton. The endoscope has a lumen extending longitudinally for receiving at least one instrument and includes means for viewing an area adjacent the distal end of the lumen. In Knighton ('043), an image of the tissue is transmitted optically through a transmission conduit from the distal end of the device to the proximal end. The image is converted to an electrical signal by an external sensor for transmission to an external monitor. The illumination source is also external and operatively connected to the transmission conduit. The fiber optic viewing and illumination portions of the endoscope are separable from the device for cleaning and reuse. The device used for the method described in Knighton ('043), however, does not include a structure on its distal end for creating an unobstructed working space near the surgical site for dissection of the vessel. The device described also must be used with a separate light source, camera, camera controller, and video monitor. This equipment costs several thousand dollars and requires cleaning and maintenance prior to each use. The portions of the visualization system within the surgical sterile field must also be sterilized or replaced prior to use on each patient, adding to the cost of the surgical procedure.
Another example of such a device is disclosed in U.S. Pat. Nos. 5,722,934 and 5,667,480, issued to Knight, et al, which are hereby incorporated herein by reference. Knight describes in '934 and '480 a method and devices, respectively, for endoscopically removing a vessel from a patient's body. A longitudinal lumen is provided in the devices so that they may be used in combination with conventional, reusable endoscopes. An incision is first made in the patient's body near the identified vessel. An optical dissector is inserted through the incision and the endoscope is then inserted into a channel running longitudinally through the optical dissector. The tissue is optically dissected away from the surface of the vessel with the optical dissector. The optical dissector has a concave head mounted on the distal end to separate tissue from the distal end of the endoscope and to create an initial space around the vessel to be harvested. The optical dissector and endoscope are then withdrawn from the body and an optical retractor is inserted into the body through the incision. The endoscope is inserted into a channel running longitudinally through the optical retractor, which is then used to retract the dissected tissue away from the surface of the vessel. A concave head attached to the distal end of the optical retractor is provided to facilitate the retraction of tissue away from the vessel. The concave head for the optical retractor is larger than the concave head for the optical dissector, and thus provides a working space around the vessel to be harvested. The vessel and its side branches are then dissected, ligated, and transected. The vessel is then removed from the body through the incision. This surgical method is especially suited for removal of the saphenous vein of the leg, to be used as a graft in a coronary artery bypass graft (CABG) procedure for the same patient. Patients who have undergone this endoscopic surgical procedure for removal of the saphenous vein in the leg have experienced significantly less pain during recovery than patients who have undergone the more traditional open surgical procedure in which an incision is made for almost the entire length of the patient's leg. Using the endoscopic procedure as compared to using the open procedure also diminishes recovery time and associated complications.
Despite the advances in the surgical art provided by the method and devices described by Knight, needing to use the devices with a separate, conventional endoscopic visualization system also presents some of the same disadvantages as noted for the instruments used in the method disclosed by Knighton. The initial costs of the capital equipment, providing space in the operating room for the equipment, maintenance, cleaning, and sterilization, all contribute to the costs for the surgical procedure. In addition, performing the endoscopic vessel harvesting procedure has an associated learning curve. Managing the conventional endoscopic imaging equipment and cables while mastering the surgical technique is an additional burden on the surgeon. Another limitation of the instruments in the prior art is access. The length of the optical retractor cannot be longer than the length of the endoscope that is inserted into the longitudinal lumen of the optical retractor. This is because the endoscope must extend to the distal end of the optical retractor to view the tissue being dissected. This length limitation may adversely affect the access of the optical retractor to the desired surgical site for some procedures.
The vessel harvesting instruments described thus far employ conventional, endoscopic imaging techniques. Conventional endoscopes are constructed such that an objective lens and an eyepiece are disposed at opposite end portions of optical fibers for transmitting an image. The image of an article to be observed is made to focus at one end face of the optical fibers and a transmitted image being transmitted through the optical fibers and appearing on the other end face is observed through the eyepiece. More recently, endoscopes have been constructed in which an image sensor is used to replace the eyepiece and convert an optical image focused on the sensor into electrical signals. The image sensor typically includes an array of light detecting elements, where each element produces a signal corresponding to the intensity of light impinging on that element when an image is focused on the array. These signals may then be used, for example, to display a corresponding image on a monitor or otherwise used to provide information about the optical image.
One very common type of image sensor is a CCD (Charged Coupled Device). CCDs have been improved greatly during the last several years, and now provide images with very good resolution. Integrated circuit chips containing a CCD image sensor, however, have a relatively low yield during manufacture and are expensive due to the specialized processing involved. The CCDs also are highly complex and consume a relatively large amount of power. A CCD also requires an array of different voltages supplied to different parts of the chip with multiple electrical power lines. Because of their size, CCDs are typically mounted on the proximal portion of endoscopic medical instruments where minimal size is less important then on the distal end of the instruments. The CCD must be used in combination with a video-processing device in order to convert the image into an electrical format that can be used by a video display. The video processing device may be constructed on a relatively small chip and mounted in the medical instrument, but the device is typically mounted inside a separate tower unit along with a power source, light source, video display, and other required components.
CCDs have low sensitivity to light and therefore require a very intense light source. Commercially available, CCD base imaging systems contain a high intensity, xenon light source in the tower unit. The light is transmitted through an optical fiber to the distal end of the instrument in order to illuminate the image. The intensity of the light transmitted is a function of the length and orientation of the optical fibers. Energy losses are very significant for optical fibers which are several feet long (in order to reach from the handheld instrument to the tower unit) and have numerous bends, such as in a flexible optical transmission cable.
A much less expensive type of image sensor is formed as an integrated circuit using a CMOS (Complementary Metal Oxide Semiconductor) process. In such a CMOS type image sensor, a photodiode or phototransistor (or other suitable device) is used as the light-detecting element, where the conductivity of the element corresponds to the intensity of light impinging on the element. The variable signal thus generated by the light-detecting element is an analog signal whose magnitude is approximately proportional (within a certain range) to the amount of light impinging on the element. An example of a medical device using a CMOS chip is given in U.S. Pat. No. 5,817,015 issued to Adair on Oct. 6, 1998, and is hereby incorporated herein by reference.
It is known to form these light-detecting elements in a two-dimensional core array that is addressable by row and column. Once a row of elements has been addressed, the analog signals from each of the light detecting elements in the row are coupled to the respective columns in the array. In some CMOS based systems, an A/D (Analog-to-Digital) converter may then be used to convert the analog signals on the columns to digital signals so as to provide only digital signals at the output of the image sensor chip. These signals may then be transmitted to a video display for viewing of the image. Examples of this type of video format include the PAL format commonly used for European televisions, and the high resolution, S video format, used, for example, in surgical operating rooms. (Most CCD based endoscopic systems also use the S video format.) Other CMOS based systems send an analog signal to the video display. An example of this type of format is the NTSC format such as used for the standard television in the United States. The latter is a very popular format, therefore, for CMOS based systems, due to the huge number of NTSC formatted televisions available.
CMOS image sensors are generally several times more sensitive to light than CCD image sensors. As a result, the light intensity required to illuminate the image when using a CMOS system (typically less than or equal to one lux) is much less than what must be provided by the light source for a CCD system. In fact, a very low power light source, such as a tungsten filament, incandescent, penlight bulb, placed near the area being imaged, or used with a short length of a light transmitting element such as an acrylic rod, is sufficient for the CMOS system to obtain a good image. The low power light source and transmitting element are small enough to place inside of a handheld, endoscopic medical instrument. The xenon light source for the CCD system, however, is necessarily larger than could be placed into an endoscopic medical instrument, and therefore is mounted into the tower unit and used with a long optical fiber transmission element having the inherent losses already described.
CMOS image sensors require very little electrical power and it is practical to use small (in the range of 6-9 VDC) batteries to operate them, although a CMOS image sensor can also be used with a conventional DC power supply connected to a wall outlet. CCD image sensors, however, require much more power to operate (typically about 60 volt-amps) transmitted through multiple power lines and it is not practical to operate them for prolonged periods of time with batteries.
From the foregoing discussion, it is evident that it would be practical and advantageous to eliminate the tower unit of a CCD based endoscopic visualization system by using instead a CMOS based visualization system. One of or both the light source and the power source can be integrated into a handheld instrument to operate the CMOS image sensor constructed into the viewing end of the instrument. The output signal of the CMOS image sensor could then be connected to any one of a number of video displays, including conventional televisions, depending on the video format chosen. By eliminating the tower unit, the capital equipment cost to the hospital of performing a surgical procedure such as saphenous vein harvesting could be greatly diminished. This would make such surgical procedures much more economically feasible in hospitals not already having the required number of expensive, endoscopic visualization systems. In addition, the space available in the typically crowded operating room could be increased. And because of the relatively low cost of CMOS based imaging devices, it would be practical to construct endoscopic surgical instruments which are single patient use disposable so that cleaning and resterilization of the instrument would not be necessary.
A surgical device is needed, therefore, for retracting, viewing, and accessing tissue, having the features and advantages of the optical retractor described in Knight ('480) and constructed integrally with a low cost, imaging sensor. Particularly, what is needed is an inexpensive, imaging retractor that incorporates a CMOS chip imaging sensor and an illumination means for viewing the tissue being operated on, thereby diminishing the need for a separate tower unit as is used with convention CCD based imaging systems.